The molecular structure of a novel siderophore produced by a PA01 strain of Pseudomonas aeruginosa was investigated . Although much of the spectroscopic and chemical properties of this compound were documented, they were insufficient for a definitive assignment of a structure to this siderophore. A partial structure has been recognized as a trihydroxyquinoline carboxylic acid whose relationship to the molecular structure of pyomerdin remains to be established.